Skid steer loaders and other work vehicles with traversing booms typically require maintenance both in the field and in a dedicated repair shop. The repairman needs access to all parts of the vehicle. Lifting the booms to an intermediate position is required, allowing manual access to the otherwise blocked area of, for example, a skid steer loader. Skid steer loader arms, or booms, are hydraulically controlled. If there are small leaks in the hydraulic system, the booms will slowly lower over time. To avoid this, there are various common mechanisms for preventing booms from lowering inadvertently. These include locking the boom control levers in the operator cab, placing a block such as a drum under the implement at the end of the booms, and locking the boom(s) itself.
In the area of boom locking devices the prior art teaches various methods of locking a boom for transport. Typically the boom is lowered against the chassis such that the chassis blocks movement in one direction and the boom lock blocks movement in the opposite direction. One example of a transport boom lock uses an operator in-cab control with a linkage to a pin or hook assembly that locks a backhoe boom against the chassis in the boom's fully upright position. While this locks the backhoe boom against all movement, it requires the boom to be in a non-working position, i.e. fully upright, as for transport. This blocks access to part of the backhoe for repair.
The prior art also teaches locks that are carried on the boom itself, either on the housing, rod or cylinder, locking the boom in an intermediate position. One example teaches a lock that is placed on the end of the hydraulic cylinder, and acts against the rod and cylinder, preventing retraction of the rod into the cylinder and thereby preventing the loader arm from lowering. This method only prevents the boom movement in one direction relative to the boom itself, that of the rod retracting into the cylinder, i.e. boom contraction.
The prior art also teaches locking pins that extend through the cab wall and extend into the plane of the skid steer loader arms, locking the booms in an intermediate position. This method prevents the loader arms from lowering with respect to the cab, but not from raising.
However, in the case of a skid steer loader with a removable combined cab and boom assembly, the situation is different. The cab and boom are tilted away from the base of the vehicle during the repair. As a result, the boom overhangs the end of the vehicle considerably. While the skid steer loader may be equipped with locking pins or sliding bars that prevent the loading arms from lowering (see U.S. Pat. No. 3,730,362 for a complete description of the layout and function of such locking pins), the weight of the cab and boom assembly will tend to pull the boom arm upwards from the cab and away from the locking pins. During repair, the implement at the end of the boom arms (bucket, rake, blade, dozer blade, etc) will typically be supported on a stand. By the force of gravity, the tilted cab boom assembly will descend toward the ground if there is a hydraulic leak, causing the boom arms to pivot upward with respect to the cab. In other words, the existing locking device only prevents the boom from pivoting downward with respect to the cab, and what is needed is a second complimentary device, or boom clamp, to prevent boom movement in the other direction. What is further needed is a simple, low cost-to-manufacture boom clamp. What is also needed is a clamp that a repairman or operator can install and remove quickly without tools when needed. What is further needed is a boom clamp that will not pinch hydraulic cables.